I had my Betta for about 4 weeks, he was beautiful! I changed his tank from a Betta tank to a 10 gallon (I was going to divide and add another one) and I added a mini heater to keep the temp right...I added the necessary chemicals to remove harmful things from the water as directed by the bottle and I also rinsed all the new accessories for the tank. He was happy! I left on vacation and left my friend in charge to watch him. Four days later he died. Now, I am not sure if I did something wrong, or if she did something wrong while I was away (I was gone for a week and he had fresh water etc the day I left) but I want to know if someone can think of anything I may have done wrong. When I came back there was food floating on top of the water and the water was super cloudy. My friend DID NOT over feed him, but I think he wouldn't eat, hence the food floating on the water. I want to get two new fishies, but I want to make sure this won't happen again!

So sorry you lost your buddy. Was he bloated when he died? If there was that much food left in the tank, chances are he ate like a pig and got constipated which could have affected his swim bladder. Or, he wasn't eating because he had internal issues.

Since you don't know what happened or whether disease is involved, you should probably break down the tank and clean it really well (no soap) before you buy more fish.